Heating-curing of rubber printing plates



Oct. 14, 1969 H. H. BUGGIE ETAL 3,

" HEATING-CURING OF RUBBER PRINTING PLATES Filed April 7, 1967 ll. a

v w V w M FIG. 1 HlGH VOLTAGE LEAD HIGH VOLTAGE 2 INVENTORS LEAD HORAQEH.BUGG\E GERALD LBANDQLPH @244 962m United States Patent ,0

3,472,989 HEATING-CURING OF RUBBER PRINTING PLATES Horace H. Buggie, 2130 Scottwood Ave., Toledo, Ohio 43620, and Gerald L. Randolph, Waterville, Ohio; said Gerald L. Randolph assignorto said Horace H. Buggie Filed Apr. 7, 1967, Ser. No. 629,209

Int. Cl. 1105b /00, 9/06 US. Cl. 219-10.67 1 Claim ABSTRACT OF THE DISCLOSURE A press having relatively movable upper and lower platens, which are electrically,v and thermally insulated from the outside, there being inductive heating means for heating the part acted upon by the press. Enclosure for the platens captures the heat when the platens are closed.

BACKGROUND OF THE INVENTION It isconventionalin'the manufacture of resilient printing plates to employ a mechanical press, the platens of which are heated by electrical resistance means. It is custornary first to produce a matrix out of a suitable resin contained within a master, usually of metal: After the matrix is formed by curing the -resin,this is used as a mold to receive a rubber compound or other thermosetting material, which is cured under heat and pressure between the platens of the press.

Such conventional procedure has been found to be objectionable for several reasons. In the first place the time required to effect the curing process for each phase consumes a period of approximately thirteen minutes. The cost factor is not inconsiderable because the expense of electrical resistance heating of the press platens is high.

A further objection which is particularly noticeable in l operation.

SUMMARY In accordance with this invention a conventional platentype mechanical press is employed for the purpose and is adapted at a minimum of trouble and expense to utilize dielectric heating. The arrangement is such that the high voltage current from a high frequency dielectric heating oscillator is delivered either to a plate electrode associated with and insulated from one of the press platens or directly to a platen itself. The resin in the master or the rubber in the matrix to be cured rests upon the other press platen which itself is grounded electrically. Thereafter the platens of the press are moved toward each other to impose a compacting pressure on the resin or rubber. According to this simple expedient, not only is the curing period for each phase reduced from approximately twelve minutes to four minutes but the operating costs represented by current consumption are reduced by approximately threefourths as compared to the conventional electrical resistance heating procedure. By appropriate insulation the loss of heat by radiation and convection are very substantially reduced so that the working conditions in the pressroom are on much more comfortable basis.

BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a sectional schematic view of a portion 3,472,989 Patented Oct. 14, 1969 DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrated embodiment of the invention comprises a portion of a platen-type mechanically driven press in which the lower platen raises and lowers relative to the upper platen. As shown, the upper platen is indicated at 10 and the lower platen at 11. The upper platen 10 is fixed to vertical rods 12 and the lower platen 11 is moved up and down by suitable means (not shown) relative to the upper platen and rides along the guide rods 12. A cup-type insulation or laminate 13 covers and is suitably secured to the bottom and side walls of the platen 10. Preferably, the insulator 13 consists of polytetrafluoroethylene such for example as marketed by Du Pont Company of Wilmington, De l., under the trade name Teflon. This insulator may be of Halon produced by Allied Chemical Company or Kel-F by Minnesota Mining & Manufacturing Company. These materials have excellent electrical and thermal insulating qualities and are found particularly useful in this connection. The lower platen 11 is similarly insulated with Teflon or the like by cupshaped insulation or laminate 14 which as shown insulates the bottom and side walls of the platen, leaving the top wall uninsulated.

Suitably secured to the under side of the insulation 13 and covering a substantial surface thereof is a flat electrically conductive plate 15, which may be of copper, aluminum or the like. The material of the plate 15 must have electrical characteristics affording a suflicient dielectric loss factor to heat to provide heat energy to the molding material in addition to the heat introduced directly through the dielectric heating effect. This plate is connected by a lead 16 to a high frequency oscillator (not shown) which may be a vacuum tube oscillator used for dielectric heating applications and having a frequency in the range of six to twenty-seven megacycles and a voltage of from one to five thousand volts.

Resting upon the top of the lower platen 11 is shown a master 17 having the desired cavities for producing a printing plate negative or matrix. The master 17 may be of metal or non-metallic material. The master 17 receives phenolic resin 18 usually in powder form and resting upon the master is a backing sheet 19 which may be of a material such as mica, alumina or Bakelite. It will be recognized that the success of dielectric heating depends upon the relationship between the electrical characteristics (di; electric constant, power factor, and loss factor) of the material making up the backing plate 19 and the resin itself. A discrete relationship between these characteristics of the two materials must be attained successfully to cure the resin. Furthermore, the backing plate must extend outward in all directions to prevent any electrical contact between the high voltage electrode 15 and the master 17. For completing the circuit the lower platen 11 is grounded by a lead 20. The press platens are brought together at once to exert the desired compacting pressure and are not separated until curing has been achieved.

By capturing the heat when the platens are brought together, efiiciency is increased. For this purpose panels of sheet metal 21, 22, 23 and 24, each faced with a panel 14 of asbestos cover the sides of the platens and form an enclosure to militate against the loss of heat. As shown except for the-panel -21 which'isconnected to the latter dielectric heating. Thus, although only the master for producing the matrix is shown on the drawings, it is to be understood that the rubber printing plate is similarly produced in the second phase of the operation. Not only is the curing time greatly reduced but also the cost of operation substantially reduced. A further advantage which is not inconsiderable is the fact that loss of heat by radiation is largely prevented due to the manner in which the platens are insulated. The insulation of the platens as above described is of particular importance not only in the retention of the heat, delivering optimum curing cycles, but also the use of the lowest possible rated dielectric heater for a selected platen area.

In the alternate form shown on FIGURE 2 the high voltage electrode plate is eliminated. Instead, the upper platen 10a is of electrically conductive material, such as copper or aluminum, and the dielectric current then is generated through the upper platen. This platen is insulated also by Teflon or similar materials in the form of an inverted cup or laminate 13 a covering the top and side walls of the platen. The high voltage lead 16a then extends directly to the upper platen 10a. It will be manifest that the remainder of the structure is similar to that above described.

Although the above description has been directed particularly to the production of resilient printing plates, it is to be understood that the invention comprehends the molding and curing of other thermosetting materials contained with a cavity or cavities in which the employment of dielectric heating in the manner set forth admissibly achieves the desired result expeditiously with unexpected economy over procedures heretofore used for the purpose. In some instances, electrical resistance heating may be employed instead of dielectric heating.

Numerous changes in details of construction, arrangement and choice of materials may be effected without departing from the spirit of the invention, especially as de- What we claim is:

1. In the curing and molding of rubber printing plates, a press having upper and lower platens movable relatively toward and away from eachother, vertical rods fixed to said upper panel, said lower panel being movable up and down on said rods, the lower platen being adapted to receive successively the master containing the resin to be cured to 'form the matrix and the matrix containing the rubber to be cured to form the printing plate, means for dielectric heating including a lead to introduce high voltage oscillating current to the region of the upper platen, an electrically conductive plate secured to the insulating material on theunderside of said upper plate and connected to said lead, means to electrically ground the lower platen, means -for electrically and thermally insulating each platen from the outside, said insulating means comprising cup-shaped thermal and electrical insulating material enclosing the bottom and sides of each of said platens, the master or matrix being adapted to rest upon said lower platen, an insulating plate covering the top of the master or matrix as the case may be, and secured to the underside of said upper platen, the material of said insulating plate having electrical characteristics atfording a sufficient dielectric loss factor to provide heat energy to the molding material in addition to the heat introduced directly through the dielectric heating effect, and asbestos lined plates carried by one platen and slidable relative to the other to provide a heat retaining enclosure when the platens are brought together.

References Cited UNITED STATES PATENTS 2,472,370 6/1949 Drugmand 219-1067 2,514,101 7/1950 Stanley 2l910.67 2,526,697 10/1950 Scott 21910.67 X 2,526,699 10/1950 Gard 21910.67 X

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner US. Cl. X.R. 219 10.s1 

